1. Field of the Invention
The present invention relates to a valve structure applied to an internal combustion engine such as an automobile engine, two-wheeled vehicle engine, utility engine or the like.
2. Related Art
There has been proposed a technology in which a valve inserted into each of a fuel gas supply line and a fuel gas discharge line in an internal combustion engine as a switching valve is made into a hollow shape and a coolant is enclosed into a hollow portion of the valve (see, for example, Japanese Laid-Open Utility Model Publication No. (1993)-50008).
Specifically, the valve disclosed in the above publication includes a hollow stem member having a shaft portion and a flare portion enlarged from the shaft portion, and a lid member welded to the flare portion so as to close the hollow portion of the stem member.
It is possible to reduce the weight of the valve by making the valve into a hollow shape as described above, thereby compacting and simplifying a coil spring for biasing the valve and a valve driving mechanism for moving the valve against a biasing force of the coil spring.
However, the conventional hollow valve does not appropriately account for elastic deformation of the valve during the combusting operation of the internal combustion engine.
That is, the valve is normally exposed to high temperature of about 450° C. when provided in the fuel gas supply line and of about 800° C. when provided in the fuel gas discharge line during the combusting operation of the internal combustion engine.
However, although the conventional valve is configured to enclose the metal natrium within the hollow portion to alleviate the temperature rise of the valve itself so that elastic deformation of the valve is prevented, it is difficult to alleviate the temperature rise to the level at which the thermal deformation of the valve is not caused only by the function of the metal natrium.
In particular, if the hollow portion is closed by welding as in the conventional valve, the internal pressure of the hollow portion is rapidly raised as the temperature is raised. The rise of the internal pressure may cause the valve to elastically deform in a large amount.
Furthermore, the pressure of the combustion chamber is raised to about 80 atm. That is, the valve may elastically deform due to the pressure rise of the combustion chamber in addition to the elastic deformation due to the temperature rise of the valve itself. In particular, in a case where the valve is made into the hollow shape, the valve has a risk of elastically deforming a large amount along the axial line direction by the pressure of the combustion chamber.
In consideration of such elastic deformation of the valve, there is provided a clearance between the valve driving mechanism and the external end of the valve. However, if the clearance is excessively wide, there is posed an inconvenience of increasing the noise when the valve driving mechanism presses the valve.
On the other hand, if the clearance is too small, the valve driving mechanism is pushed up by the valve due to the elastic deformation of the valve, resulting in damaging a cam member forming the valve driving mechanism and the like.